METHOD OF MANUFACTURING A WELDING STUD

Abstract

A method of manufacturing a welding stud. The welding stud comprises a weldable portion of light metal and a functional portion of steel. The method comprises the steps of: providing a welding part of a light metal and partially defining a recess, providing a function part of a steel and which includes a protrusion, providing a press with a die and a punch, arranging the welding part on the die and the function part on the press such that the protrusion opposes the recess, and manufacturing the welding stud by impacting the welding part and the function part into the die by the punch such that the protrusion enters the recess and the welding portion forms a sleeve around an end of the function portion to form the welding stud with the welding part forming the weldable portion and the function part forming the functional portion.

Claims

1. A method of manufacturing a welding stud adapted to be welded to a workpiece and the welding stud comprises a weldable portion of light metal and a functional portion of steel, wherein the method comprises the following steps: a. Providing a welding part of a light metal, wherein the welding part partially defines a recess; b. Providing a function part of a steel, wherein the function part includes a protrusion; c. Providing a press with a die and a punch; d. Arranging the welding part and the function part on the press such that the protrusion opposes the recess; e. Manufacturing the welding stud by impacting the welding part and the function part into the die by the punch such that the protrusion enters the recess and the welding portion forms a sleeve around an end of the function portion to form the welding stud with the welding part forming the weldable portion and the function part forming the functional portion.

2. The method according to claim 1, wherein the function part comprises a shank extending along a longitudinal axis, a press-fit area and a flange arranged axially between the shank and the press-fit area, and the flange extends radially outwardly from the shank.

3. The method according to claim 2, wherein the shank further comprises a threaded portion distal from the press-fit area.

4. The method according to claim 3, wherein the arranging step the shank is arranged on the punch and the welding part is arranged on the die.

5. The method according to claim 2, wherein the press-fit area is the protrusion and the protrusion defines a frusto-conical shaped section with a smaller-diameter end proximal to the flange and a larger-diameter distal from the flange.

6. The method according to claim 5, wherein the outer surface of the protrusion extends with an angle between 2 and 7 degrees with regard to the longitudinal axis.

7. The method according to claim 1, wherein the die includes a die cavity with a chamfered edge.

8. The method according to claim 1, wherein the die includes a die recess closed by an ejector pin.

9. The method according to claim 8, wherein the ejector pin is tapered to form a tip on the function portion.

10. The method according to claim 1, wherein the welding part is an aluminium material.

11. The method according to claim 2, wherein the press-fit area is the protrusion and the protrusion defines a frusto-conical shaped section with a smaller-diameter end proximal to the flange and a larger-diameter distal from the flange.

12. A weld stud adapted to be welded to a workpiece, the weld stud comprising: a weldable portion of a light metal and which partially defines a recess; a functional portion of a steel and which includes a protrusion; and the weldable portion and the functional portion are arranged with the protrusion axially opposed to and extending into the recess; and the weldable portion forms a sleeve around an end of the functional portion.

13. The weld stud according to claim 13, wherein the functional portion further includes a shank extending along a longitudinal axis, a press-fit area, and a flange arranged axially between the shank and the press-fit area, and the flange extends radially outwardly from the shank.

14. The weld stud according to claim 14, wherein the shank further includes a threaded portion distal from the press-fit area.

15. The weld stud according to claim 13, wherein an outer surface of the protrusion extends with an angle between 2 and 7 degrees with regard to a longitudinal axis.

16. The weld stud according to claim 13, wherein the light metal is an aluminium material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Other characteristics and advantages of the invention will readily appear from the following description of embodiments, provided as non-limitative examples, in reference to the accompanying drawings.

[0029] FIG. 1 schematically shows a welding stud according to a first embodiment with a welding portion and a function portion.

[0030] FIG. 2 schematically shows a welding part and a function part in a press with a die and a punch before pressing the welding part and the function part to realize the welding stud of FIG. 1.

[0031] FIG. 3 schematically shows the welding stud of FIG. 1 with a welding portion formed by the welding part and a function portion formed by the function part after impact extrusion.

[0032] FIG. 4 shows a welding part and a function part before impact extrusion according to a second embodiment.

[0033] FIG. 5 shows the welding stud with a welding portion formed by the welding part of FIG. 4 and a function portion formed by the function part of FIG. 5 after impact extrusion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] On the different figures, the same reference signs designate identical or similar elements.

[0035] FIG. 1 and FIG. 5 show two embodiments of a welding stud 10, 10, and more particularly of a hybrid welding stud. The welding stud 10, 10 comprises a welding portion 12, 12 and a function portion 14, 14. The welding stud 10, 10 is adapted to be welded to a workpiece, for example to a vehicle body. More particularly the welding portion 12, 12 of the welding stud 10, 10 is welded to the body vehicle, whereas the function portion 14, 14 is adapted to be connected to different components. The welding portion 12, 12 and the function portion 14, 14 are made in two different materials.

[0036] For instance, the welding portion 12, 12 is made of a good weldable material such as aluminium alloy, whereas the function portion is made of steel material.

[0037] The welding portion 12, 12 is made from a welding part 120, 120, whereas the function portion 14 comes from a function part 140, 140. The welding part is made in a first material, and notably in light-weight material such as aluminium. The function art is made of steel.

[0038] More particularly, in order to manufacture the welding stud of FIG. 1 or FIG. 4, the function part 140, 140 and the welding part 120, 120 are joined together by impact extrusion. The impact extrusion is a cold forming process. A die D and a punch P are used to press at an extreme force and/or a high velocity the function part 140, 140 against the welding part into the die D. For instance, the function part 140, 140 or the welding part 120, 120 is placed in the die D (also called mold). The welding part 140, 140 or function part 120, 120 in the die is struck with a great force by the function part or the welding part. The material of the part in the die then flows into a predetermined position in order to form the hybrid welding stud 10. 10.

[0039] For instance, for the welding stud 10 of FIG. 1, the function part 140 impacts the welding part 120 at such a force that it allows the welding part notably to be transformed into a plastic state that allows the welding part to flow into the die and around the function part.

[0040] Before the cold forming process, the welding part 120 and the function part 140 are independent from each other. After the cold forming process, both parts are fixedly joined to each other.

[0041] As illustrated in FIG. 1, FIG. 3 or FIG. 5, the welding portion 12, 12 comprises a top section 16, 16 adapted to be welded to the workpiece. The top section 16, 16 is adapted to form a weld nugget. The top portion 16, 16 may be flat or may be provided, as illustrated in FIG. 1 and FIG. 5, with a tip 18, 18. The tip 18, 18 improves the welding process of the welding stud 10, 10 to the workpiece. More particularly, the surface of the top section 16, 16 may have a conical shape with the edge of the cone being the tip 18, 18. In other embodiments, the top portion comprises several portions extending non-parallel to each other and which form the tip.

[0042] The welding portion 12, 12 comprises a rear section 20, 20 opposite the top section 16, 16. The rear section 20, 20 is adapted to face the function portion 14, 14.

[0043] The top section 16, 16 is formed by a top section 160, 160 of the welding part 120, 120. The rear section 20, 20 is formed by a rear section 200, 200 of the welding part 120, 120.

[0044] In the first embodiment, illustrated in FIG. 2, the rear section 200 is provided with a recess 220. The recess 220 is a blind hole and not a through hole. The recess 220 comprises a circular cross-section with lateral walls extending around a recess axis Xr. The recess comprises a recess diameter Dr and a recess length Lr. The recess is surrounded by lateral walls having a thickness Th. The bottom of the recess is destined to form the welding nugget.

[0045] In the embodiment of FIG. 2, the function part 140 extends along a longitudinal axis X between a first end section and a second end section. The function part 140 comprises a shank 141 extending along the longitudinal axis X, a press-fit area 143 adapted to cooperate with the recess 220 and a flange 142 arranged between the shank 141 and the press-fit area 143, wherein the flange 142 extends radially outwardly from the shank 141.

[0046] The shank 141 comprises a screwthread portion.

[0047] The press-fit area 142 is a protrusion. More particularly the press-fit area 142 is formed by the continuity of the shank beyond the flange. For instance, the protrusion comprises a frusto conical shape with the smaller-diameter end extending from the flange and the larger-diameter end being a free end. The protrusion comprises a protrusion length Lp along the longitudinal axis X. The outer surface of the protrusion extends with an angle between 2 and 7 deg. with regard to the longitudinal axis. For example, the angle is of sensibly 5 degrees.

[0048] The protrusion is adapted to be arranged in the recess 22 just before the cold forming process, as illustrated in FIG. 2. The larger diameter of the protrusion is smaller than the recess diameter. The protrusion length Lp is greater than the recess length Lr.

[0049] For the impact extrusion process, the welding part 120 is arranged in the die D (or a mold). The die is for example located on a mechanical or hydraulic press. More particularly, the die D has an inner wall defining an extrusion cavity C. The cavity C comprises a bottom end. The shape of the extraction cavity corresponds to the size required for the generation of the welding portion.

[0050] The bottom end can include a protruding point for generating a dimple in the welding portion. The bottom end can be partially or completely formed by an ejector pin 150, allowing a better ejection of the welding stud once formed.

[0051] The free end of the inner wall can be chamfered, allowing a better cold forming and a better ejection. The welding part is disposed for instance on the chamfered edge.

[0052] The press comprises also the punch P. The punch P is securely connected to the function part 140, such that the punch and the function part form together a punching unit. A portion of the punching unit is receivable in the die D. More particularly, the protrusion is receivable in the die D. The manufacture of the welding stud can be performed by advancing the punching unit into the recess 220 with sufficient force to extrude metal from the welding part between the punching unit and the die to form the desired welding portion, as depicted in FIG. 3. The welding portion 12 thus form a tube or a sleeve around the protrusion.

[0053] More particularly, after the cold forming, the welding portion 12 entirely surrounds the protrusion and abuts against the flange 142. The shape and the size of the recess gives the shape and the size of the welding portion formed. The chamfered edge allows the welding portion 12 to form a slope in the direction of the flange, such that the surface of the flange facing the protrusion is entirely covered by the welding portion. The thickness of the welding portion around the protrusion is sensibly constant. The bottom of the welding portion (which forms the top section 16) is thick enough to be welded to a workpiece without undamaging or interfering with the function portion.

[0054] In the first embodiment, the cold forming modifies the shape of the welding part 120 to form the welding portion 12, whereas the shape of the function part 140 remains sensibly unchanged and corresponds to the shape of the function portion 14.

[0055] In the second embodiment, in reference to FIGS. 4 and 5, the shape of both the function part 120 and the welding part 140 is modified during cold forming to form the welding stud.

[0056] As illustrated in FIG. 4, before cold forming, the function part 140 comprises a recess which form the press-fit area 143. The flange 142 forms the bottom of the recess. The recess is defined by lateral walls W. The lateral walls W comprise an inner surface 144, an outer surface 145 opposite the inner surface. The inner surface 144 extends sensibly parallel to the longitudinal axis X. The outer surface 145 extends radially outwardly tapered from the flange. More particularly, the outer surface of the wall forms in cross section an angle g. The recess 143 comprises a circular cross-section and has a recess diameter. The flange can be a sphere or a hemisphere.

[0057] The welding part 120, in the second embodiment is a token having a first section 121 with a first diameter adapted to be inserted in the recess of the function part, and a second section 122 with a second diameter, larger than the first diameter and adapted to remain outside the recess. The first diameter and the recess diameter are substantially similar. The interface between the first section and the second section forms an elbow 123 and the edge of the lateral walls of the function part is adapted to rest against said elbow.

[0058] During the cold forming, the lateral walls W of the recess are pressed radially in the direction of the token, and more particularly in the direction of the first section. By pressing the lateral walls in the direction of the first section, the token is deformed. The free end of the lateral wall W anchors in the first section. The deformation of the function part 140 can be such that, the outer surface of the lateral wall extends sensibly parallel to the longitudinal axis X after the cold forming. For instance, after the cold forming, the inner surface of the lateral wall defines in cross section an angle h.

[0059] During the impact extrusion, it is to be noted that the flange 142 and more particularly the support surface of the flange facing the shank 141 is not deformed. Thus, the diameter of the flange Df remains unchanged before and after cold forming. For this purpose, the diameter of the second section of the token Db, the diameter of the flange Df, the end diameter of the lateral wall after deformation Dd, and the thickness of the flange along the lateral axis X are specially matched to one another. For instance, as depicted in the drawings, the end diameter of the lateral wall after deformation Dd is greater than the diameter of the flange Df. Besides, the end diameter of the lateral wall after deformation Dd is greater than the diameter of the second section of the token Db. The recess diameter is smaller than the end diameter of the lateral wall after deformation Dd. More particularly, the ratio between the recess diameter (or the first diameter) and the end diameter of the lateral wall after deformation Dd is between 0.2 and 0.9. For instance the ratio is of 0.8.

[0060] The angle g is chosen so that it generates sufficient pressure in the formed state (angle h) to hold the token in the function part. The angle g is for example between 15 and 35 degrees, or between 20 and 30 degrees and more particularly the angle g may be of 26 degrees.

[0061] The longitudinal length f between the supporting surface of the flange 141 and the outside edge of the second section of the welding part is to be matched with the final length e between the supporting surface of the flange 141 and the outside edge of the second section 122 of the welding portion.

[0062] By increased torsional loading, the functional part 140 (more particularly in the recess) and the welding part 120 (only the first section 121, not the second section designed to form the welding nugget) can be arranged with a particular contour, which avoids twisting of the aluminium to steel component under torque loading, e.g. hexagonal shaper, internal serration, hexagon or octagon. Alternatively, the cold forming operation may be performed on the outer surface of the lateral wall to create for instance a polygon contour. The shape is then transferred from the function portion 14 to the welding portion 12 and thus a positive connection of the function parts and welding parts is generated and prevents rotation of the components to each other.

[0063] Although exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.